Abstract
Thiamine deficiency is a large contributor to reduced reproduction success among salmonids throughout the northern hemisphere. In Scandinavia, this reproduction disorder is known as M74; while in North America, it is known as early mortality syndrome (EMS). The disorder fluctuates in magnitude from year to year. During years with high prevalence of the disorder, salmonid hatcheries that stock various aquatic systems to maintain the population size experience difficulties filling their quotas without thiamine treatment of alevins. The disorder is monitored both by observing the survival rate and by measuring the thiamine content of prefertilized eggs in the hatcheries. Here, a simple extraction procedure is presented, which allows for quantitative determination of the various phosphorylated forms of thiamine using liquid chromatography mass spectrometry but also allows for extraction in 96 deep-well plates and measurement of the total thiamine content using fluorescence monitoring with a plate reader, following oxidation of thiamine to thiochrome. The latter procedure could also be integrated into a highly portal system where the thiochrome is determined using the DeNovix QFX analyzer. The newly developed extraction procedure and cleanup method for fluorescence measurement represent the most versatile and simple methods to date for monitoring of thiamine in salmonid eggs. The methods produced accurate and precise data with quantification limits below the limit where the deficiency causes 100% lethality.